Heretofore, a fuel cell system including a fuel cell which receives supply of reactive gases (a fuel gas and an oxidizing gas) to generate a power has been suggested and put to practical use. In recent years, a fuel cell system has been suggested in which a fuel supply channel for supplying, to the fuel cell, the fuel gas supplied from a fuel supply source such as a hydrogen tank is provided with a variable gas supply device such as a mechanical type variable regulator or an injector, whereby a pressure of the fuel gas to be supplied from the fuel supply source can be changed in accordance with an operation state of the system (e.g., see Japanese Patent Application Laid-Open No. 2005-302563).